Transsphenoidal surgery has long been proven as the treatment of choice for patients with Cushing's disease. Debate, continues, however, regarding the criteria used to define surgical cures versus those patients that may require further surgery and/or radiation therapy. The goal of this study is to evaluate serum cortisol before and following transsphenoidal surgery in order to elucidate the pattern of cortisol decrease and the optimal time and criteria for determining surgical cure.